The present invention relates to a flying-type composite magnetic head for use in a magnetic disk drive in such a manner that it is slightly floating over a magnetic recording medium, and a method of producing the composite magnetic head.
As magnetic heads used for writing and reading information in magnetic disk apparatuses, flying-type magnetic heads as shown in U.S. Pat. No. 3,823,416 and Japanese Patent Publication No. 57-569 are widely used. Such a flying-type magnetic head is constituted by a slider, a tail end of which is provided with a magnetic gap, and the overall slider body is constituted by an oxide-type magnetic material with high permeability.
The flying-type magnetic head is in light contact with a magnetic disk by a spring force when the magnetic disk is stationary. When the magnetic disk is rotating, a flow of air over the magnetic disk exerts an upward force to a lower surface of the slider, whereby the magnetic head floats over the magnetic disk. When the magnetic disk starts to rotate or stops, the magnetic head comes into sliding contact with the magnetic disk. Here, the contact condition of the magnetic head with the magnetic disk when the magnetic disk is stopped will be explained in detail. First, the flow of surface air becomes gradually slow when the rotation speed of the magnetic disk is reduced. When the magnetic head loses its floating force, it collides with the disk surface and jumps up by its reaction and then falls onto the disk surface again. Such movement is repeated and the magnetic head slides on the disk to finally stop. Accordingly, the magnetic head should withstand shocks at the time of start and stop, and such characteristics are sometimes called CSS characteristics (contact start stop characteristics).
Flying-type magnetic heads are generally constituted by ferrite which is an oxide-type magnetic material with high permeability have relatively good CSS characteristics. However, the ferrite has a small saturation magnetic flux density, so that sufficiently high recording densities cannot be achieved to recording media having high coercive forces. Specifically, even with use of a Mn-Zn ferrite having a relatively high saturation magnetic flux density Bs, its Bs is at most 5000 G or so.
It was then found that to achieve Bs of 8000 G or more, a magnetic head is desirably provided with a thin magnetic metal layer in its magnetic gap. For instance, Japanese Patent Laid-Open No. 58-14311 proposes a flying-type magnetic head composed of ferrite and provided with a magnetic metal layer with high saturation magnetic flux density only in a magnetic gap portion thereof. However, in this magnetic head, a magnetic transformation part has large inductance after provided with coil windings, so that it has low resonance frequency. This means that it is disadvantageous in recording and reproducing at high frequency. Here, the large inductance is due to the fact that the overall magnetic head is composed of a magnetic material.
Accordingly, to achieve low inductance, a magnetic circuit should be made small. From this point of view, U.S. Pat. No. 3,562,444 discloses a flying-type composite magnetic head in which a magnetic core is embedded in and fixed to a non-magnetic slider, without constituting the entire magnetic head with a magnetic material.
Further, the present inventors proposed in Japanese Patent Laid-Open No. 61-199219 a flying-type magnetic head in which a magnetic core is embedded in a non-magnetic slider.
It has been found from the above that to obtain a flying-type composite magnetic head having good recording characteristics to high-coercive force recording media and small inductance, composite magnetic core should be constituted by a Mn-Zn ferrite substrate with a high saturation magnetic flux density Bs and coated with a thin magnetic layer having high Bs in its magnetic gap portion. Such a magnetic core should then be embedded in a non-magnetic slider.
Gap structures of magnetic cores assembled in such flying-type composite magnetic heads are known as an X-type as proposed by Japanese Patent Laid-Open No. 61-199217 and a so-called parallel type which has a notch for regulating a track width on a track surface of a magnetic core. Both the X-type and parallel-type magnetic cores are constituted by I-shaped core pieces and C-shaped core pieces. The I-shaped core pieces are formed with thin magnetic metal layers made of Fe-Al-Si, etc. Incidentally, the parallel-type magnetic cores are advantageous in that their magnetic gaps are easily formed and their track widths are precisely regulated.
However, since the thin magnetic metal layer and the core piece generally have largely different thermal expansion coefficients, the thin magnetic metal layer tends to peel off from the core piece, or the core pieces are likely to be cracked due to internal stress in a bonding portion with the thin magnetic layer, when the core pieces are bonded with each other by glass, or when the magnetic core is fixed to a non-magnetic slider. If cracking takes place in core pieces from which thin magnetic layers peel off, reproduction characteristics are deteriorated to a pseudo-gap effect which causes small peaks (subpeaks) to appear in other regions than signal regions.
Various attempts have been made to solve the above problems. For instance, to prevent the problems of peeling and cracking due to the difference in thermal coefficient between the core pieces and thin magnetic metal layer a thinning of the metal layer is considered. However, it is not preferable to make the metal layer extremely thin because it leads to the deterioration of its magnetic properties.
In the production of such a flying-type composite magnetic head, a C-shaped core piece and an I-shaped core piece are first bonded to each other to form a magnetic core, and the magnetic core is inserted into a slit of a non-magnetic slider with a glass rod placed thereon, and heated at high temperature to cause the glass to flow into a gap between the magnetic core and the non-magnetic slider. As a result, the magnetic core is fixed to the slider. However, if the heating temperature is too high, a gap portion of the magnetic core formed with a glass would be loosened or expanded, resulting in the deterioration of magnetic head characteristics. Accordingly, in the bonding of the magnetic core, a low-melting point glass should be used. Conventionally used as a low-melting point glass is typically the following glass:
______________________________________ Corning Glass 8463 ______________________________________ Softening point 377.degree. C. Thermal expansion coefficient 105 .times. 10.sup.-7 /.degree.C. (25-310.degree. C.) ______________________________________
However, since this low-melting point glass has poor strength, cracking easily takes places even with a small difference in the thermal expansion coefficient. In addition, it has poor resistance to environmental conditions and is susceptible to discoloration, etc.
The inventors of the present invention thus proposed in Japanese Patent Laid-Open No. 60-243182 a glass for bonding magnetic cores made of Mn-Zn ferrite, a ferromagnetic oxide, to a non-magnetic slider, which has a composition of:
______________________________________ SiO.sub.2 : 9-12 weight %, B.sub.2 O.sub.3 : 3-9 weight %, Al.sub.2 O.sub.3 : 3-6 weight %, and PbO: 76-82 weight %. ______________________________________
This bonding glass has a softening point of 404.degree.-446.degree. C. and a thermal expansion coefficient of 87.6-96.4.times.10.sup.-7 /.degree. C. (30.degree.-280.degree. C.).
Although the above low-melting point glass has a sufficiently low melting point for bonding magnetic cores, it is not necessarily satisfactory in corrosion resistance, particularly in acid resistance and water resistance. Accordingly, in the process of washing after assembling, discoloration may take place, and large steps may be generated between the surfaces of the magnetic core and the slider and the glass surface.
On the other hand, with respect to a glass for bonding magnetic cores, if it has too high a softening point, a first bonding temperature, at which core pieces are bonded together, also becomes too high, thus causing the peeling of thin magnetic metal layers. Also, if it has too low a yielding temperature, magnetic gaps may change in the process of second bonding for fixing the magnetic cores to non-magnetic sliders.